Acceleration control valve

ABSTRACT

An acceleration control valve for a hydrostatic transmission having a pump, a motor, a high pressure fluid conduit, a low pressure fluid conduit and a fluid by-pass in parallel around the motor from the high to the low pressure conduit. The acceleration control valve controls the fluid flow through the by-pass and thus regulates the application of fluid to the motor. The valve is normally open allowing a portion of fluid from the pump to bypass the motor. Upon pressurization of the high pressure conduit the control valve gradually closes as fluid flows through the bypass thus providing a gradually increasing amount of fluid to the motor which results in smooth and gradual acceleration of the motor.

United States Patent [151 3,704,588 Trabbic 51 Dec. 5, 1972 [54]ACCELERATION CONTROL VALVE 72 Inventor: Gerald w. Trabbic, Marshall,Mich. hammer-Edgar Gwghega" Attorney-Teagno .& Toddy [73] Assignee:Eaton Corporation, Cleveland, Ohio 22 Filed: April 1, 1971 [571 ABSTRACT[21] APPL NM 130,361 An acceleration control valve for a hydrostatictransmlsslon having a pump, a motor, a hlgh pressure fluld conduit, alow pressure fluid conduit and a fluid by- [52] US. Cl. ..60/53 R, 60/52B, 137/1 15, pass in parallel around the motor from the high to the417/299 low pressure conduit. The acceleration control valve [51] 1111;. Cl ..F16C] 31/00. controls the fluid flow through the by pass andthus [58] Fleld of Search "60/53 52 137/115 regulates the application offluid to the motor. The 417/299 ,valve is normally open allowing aportion of fluid from the pump to by-pass the motor. Upon pressurizationof [56] References C'ted the high pressure conduit the control valvegradually UNITED STATES PATENTS closes as fluid flows through the by-pass thus providing a gradually increaslng amount of fluld to the motor2,058,894 l0/l936 Llnk .....60/53 R which results in Smooth and gradualacceleration of 2,852,9l8 9/1958 Schwary ..60/53 R X the motor 3,402,5499/1968 Connett et al ..60/19 3,522,999 8/1970 Liles ..417/299 9 Claims,6Drawing Figures ELECTRIC MOTOR LOW PRESSURE FIELD OF THE INVENTION Thisinvention relates generally to hydrostatic transmissions of the typehaving a motor and a pump, one or both of which may be of .the variabledisplacement type. More particularly, this invention relates to anacceleration control valve for providing smooth acceleration anddeceleration of the motor of a hydrostatic transmission as thetransmission is shifted to and from its neutral condition.

DESCRIPTION OF THE PRIOR ART Heretofore, hydrostatic transmissions havesuffered from a tendency to jerk when shifted to or from their neutralcondition. This tendency is especially pronounced when there is arelatively light load to be moved as is the case in a garden tractorapplication or the like. This sudden change in acceleration, or jerk,has a very detrimental effect on the transmission, the

mechanical parts of the machine being controlled and,

of course, the load. Earlier attempts to solve this problem haveinvolved complicated and expensive hydraulic and/or mechanical linkagesystems. These systems have been less than satisfactory as they areexpensive to produce and difficult to maintain.

SUMMARY OF THE INVENTION trol valve which controls the flow offluid'through the by-pass. I The progressively decreasing by-pass flowaround themotor results in smooth and controlled ac-. celeration of themotor. I r

In a hydrostatic transmission including a pump, a motor and fluidconduits therebetween, an acceleration control valve is provided in abyf-pass interconnection between the fluid conduits. The accelerationcontrol valve controls the mass flow rate of fluid permitted to by-passthe motor of a hydrostatic transmission when that transmission isshifted to or from its neutral condition. The valve is normally open andis spring biased to that position. The valve comprises a body with apiston member slidably disposed therein to control the flow of fluidtherethrough. The piston has two opposing faces of different areasexposed to fluid pressure and is normally biased by spring force andpressure acting on the to flow to the motor and thus assure smoothaccelera' tion of the motor.

An object of this invention is to provide a new and improvedacceleration control for hydrostatic transmissions.

Another object of this invention is to provide a new and improvedhydrostatic transmission having smooth and gradual acceleration. A

Another object of this invention is to provide a hydrostatictransmission having a by-pass around the motor which permits a graduallydecreasing flow of fluid therethrough as the transmission is shifted toor from its neutral condition resulting in smooth acceleration of themotor.

Another object of the invention is to provide a new and improvedhydrostatic transmission having a fluid by-pass around the motor forgradually increasing the flow of fluid to the motorresulting in smoothacceleration of the motor.

A further object of this invention is to provide a new and improvedacceleration control valve of inexpensive cost.

Further objects and advantages of the present invention will be apparentfrom the following description and reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic view of ahydrostatic transmission utilizing the invention of the presentapplication.

FIG. 2 is a cross-section of the acceleration control valve of thepresent invention.

FIG. 3 is a detailed cross-section of the piston member of theacceleration control valve of FIG. 2.

FIG. 4 is a cross-section of an acceleration control valve embodying thefeatures of the present invention utilizing a modified piston. FIG. 5 isa schematic view of a modified embodiment of the present invention.

FIG. 6 is a schematic view of a further modified embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, thehydrostatic transmission system may be seen generally at 10. Hydrostatictransmissionsystem 10 includes a fixed displacement fluid motor 12 whichis drivingly connected to a load 14. A variable displacement fluid pump16 which is driven by a constant speed external source, such as anelectric motor-18, is connected to the fluid motor 12 by first andsecond conduits '20, 22. It is understood that a fixed displacementmotor variable displacement pump type of transmission is used forillustrative purposes only and that this invention is equally applicableto fixed displacement pump variable displacement motor transmissions andthe like. In the embodiment shown, the variable displacement pump 16 hasspeed and direction control means 24 for'controlling the output of thepump 16 which is shown in the F or forward position. By design, conduit20 will be a high pressure conduit delivering high pressure fluid fromthe pump 16 to the motor 12 and conduit 22 will be a low pressureconduit returning fluid from the motor 12 to the pump 16 when thecontrol means 24 is in the position control valve 28. The by-pass 26includes a one-way check valve 29. The acceleration control valve 28, bycontrolling the flow rate of fluid to the motor 12, provides a smoothacceleration upon engagement of the transmission from the neutralposition, N. The hydraulic transmission may also include a by-passsystem 26' with control valve 28 for controlling the acceleration of thetransmission in both its forward and reverse modes of operation.Acceleration control valves 28 and 28' are normally open, thus allowingfluid to by-pass the motor from the high pressure to low pressureconduit. The valves will gradually close as fluid flows through theby-pass thus providing a gradually increasing flow of pressurized fluidto the motor 12 which will result in gradually increasing and smoothacceleration, saving wear and tear on the transmission, the power sourceand the load. I

Referring to FIGS. 2 and 3, acceleration control valve 28 is shown ingreater detail. The valve 28 is shown as interposed in series betweenhigh pressure conduit and low pressure conduit 22 in a by-pass loop 26.The valve 28 comprises a hollow cylindrical housing 30 having a largerinterior diameter bore 32 and an axially adjacent smaller interiordiameter bore 34. An inlet 36 to bore 34 and an outlet 38 from bore 32define the fluid flow path through the valve. An end portion 40 of thehousing 30 seals the left hand end of bore 32 in the housing 30.Slidably mounted within the valve housing 30, in sealing relation withthe bores 30 and 32' is a differential area piston 42, see FIG. 3.Piston 42 has sections 44 and 46 of different exterior diameter whichcorrespond with the interior diameter of bores 34 and 32 of the housing30 respectively. The piston 42 hasan axially'extending bore 48 openingat its righthand end and a smaller restricted orifice 50 whichcommunicates the bore 48 with the pistons lefthand end. Radial bores52extend from the axial bore 48 to the exterior surface 44 of piston 42.The piston 42 is normally biased to the left as in FIG. 2 by a spring54, so that by-pass 26 is normally open permitting flow from highpressure conduit 20 to low pressure conduit 22 when the pump 16 is inneutral condition or first shifted from neutral condition.

In operati'omstarting from theneutral condition, the pump 16 is placedinto the forward position F which causes a large volume of high pressurefluid to flow through conduit 20 toward motor 12. Due to the largerpressure differential across by-pass 26 then across motor 12 a largepercentage of this fluid will by-pass the motor and flow into by-passloop 26. The remainderof the fluid will continue in conduit 20 to themotor 12 for'operation thereof. The fluid entering bypass loop 26 willenter valve bore 34 through inlet 36 loop 26. The gradual sealing ofradial bores 52 provides a variable fluid flow orifice for controllingthe flow rate of fluid through by-pass 26. Thus the motor 12 willgradually receive an increasing flow of fluid from pump 16 and willexperience a gradual and smooth acceleration until the entire volume offluid from the pump I6 is passing through the motor 12. The rate atwhich bypass loop 26 is gradually closed may be varied by simplevariations of spring 54. I I

MODIFICATION I FIG. 4 shows a modified valve ,128 of the presentinvention using a modified piston 142. Fluid flow through the valveisfrom inlet 136, past the variable fluid flow orifice 159 formed by thegap between conical surface 160 of the piston 142 and the corner 162 ofthe housing 130, and out the outlet 138. As the piston 142 moves to theright the orifice becomes gradually increasingly restricted until itfinally blocks flow through the valve 128 completely. The taperedsurface 160 provides an exceptionally smooth acceleration of the motor12, by producing an infinite variation in the fluid flow path at orifice159.

MODIFICATION II FIG. 5 shows a ba'ck-to-back valve arrangement wherein asingle bypass loop 226 is utilized to bypass fluid around the motor 12both from 20 to 22 and from 22 to 20 depending upon which of theconduits, 20 or 22, is in the high pressure mode. In this arrangementvalves 28 and 28 have their outlets 38 and 38 interconnected by conduit280. i

In operation, assuming conduit 20 to be the high pressure conduit, fluidflowing out valve outlet 38 will flow through conduit 280 into valve 28'outlet 38, from there the fluid will flow through bore 52' into bore 48'and out inlet 36' into conduit 22. When conduit 22 is the high pressureconduit, fluid flowing out valve outlet 38 into valve outlet 38 willfollow a similar flow path.

MODIFICATION III FIG. 6 illustrates another modified form of theinvention in which fluid is by-passed from high pressure conduit 20directly to a reservoir. 390 by means of by-pass and then flow intoaxial piston bore 48. The majority of fluid in piston bore 48 will flowout radial bores 52 into valve bores 32 and then to low pressure conduit20 through outlet 38. A smaller portion of the fluid in axial bore 48will flow through restricted orifice 50 to act upon larger piston face56 of piston 42. The force of will graduallyseal radial bores 52 invalve bore 34 and thus gradually restrict fluid flow through the bypass326 controlled by acceleration control valve 328 which operates in thesame manner as previously described valve 28.

Although this invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

I claim:

1. A hydrostatic transmission with controlled acceleration comprising:

a pump for supplying pressurized fluid;

a motor in fluid communication with said pump;

a by-pass in fluid communication with said pump for diverting a portionof the fluid from said pump away from said motor, said motor and saidby-pass connected in parallel to said pumpjand I06009 I oosscontrolmeans in said by-pass for controlling the flow of fluid throughsaid by-pass, said means being normally open and operable to graduallyclose said by-pass and restrict fluid flow therethrough for graduallyincreasing the flow of fluid to said motor, said control meanscomprising:

a housing having an inlet and an outlet connected in series in saidby-pass, said housing having a first bore adjacent said inlet and alarger bore adjacent said outlet, said first and larger bores beingconcentric and axially adjacent;

a differential area piston having first and second opposed faces ofsmaller and larger areas respectively slidably disposed within saidbores, said piston biased by a spring and fluid pressure actingon saidfirst face to a first position whereat the piston allows fluid to flowfrom said inlet to said outlet, said piston biased by fluid pressureacting on said second face to gradually overcome the bias of said springand fluid pressure acting on the first face to move to a second positionwhereat said inlet is blocked from saidoutlet, said piston comprisingaxially adjacent first and larger exterior diameter sections slidablyand sealingly engaged in said first and larger bores respectively, saidfirst section carrying said first face and said larger section carryingsaid second face, said piston having an axial bore communicating withsaid inlet and a radial bore communicating said axial borewith theexterior surface of said first section, said radial bore communicatingwith said outlet in said first position and sealed by said first bore insaid second position.

2. The transmission of claim 1 wherein said piston additionallycomprises a restricted fluid passageway communicating said axial borewith said second face.

3. The transmission of claim 1 wherein said piston comprises a largerexterior diameter section sealingly and slidably disposed in said largerbore and an axially adjacent tapered section of decreasingcross-sectional diameter towards said inlet, said larger diametersection carrying said second face and said tapered section carrying saidfirst face, said piston moving toward said inlet when moving from saidfirst to said second position to form said variably restricted fluidflow orifice between the outer surface of said tapered section and theinterior of said first bore.

4. The transmission of claim 3 wherein said piston additionallycomprises a restricted fluid passageway communicating said inlet andsaid second face.

5. A hydrostatic transmission having controlled acceleration comprising:

a reversible pump,

a reversible motor,

first and second fluid conduits connecting said pump to said motor;

a first and second one-way by-pass connected in parallel around saidmotor, said first by-pass operable to bypass fluid around the motor fromsaid first to said second conduit when said first conduit is at a higherpressure than said second conduit, said second by-pass operable toby-pass fluid around the motor from said second to said first conduitwhen said second conduit is at a higher ressure than said first conduit,and a first an second acceleration control valve for controlling theflow of fluid through said first and second by-pass respectively, saidcontrol valves connected in series in said by-passes and being normallyopen and operable to gradually close as fluid flows therethrough.

6. The transmission of claim 5wherein said control valves comprise:

a hollow housing having an inlet and an outlet, connected in series insaid by-passes, said housing having an axially adjacent smaller interiordiameter bore adjacent said inlet and a larger interior diameter boreadjacent said outlet;

and a piston slidably disposed within said housing for controlling theflow of fluid between said bores by providing a variably restrictedfluid flow orifice therebetween, said piston in a first positionproviding maximum fluid flow through said orifice and in a secondposition blocking said orifice;

means for biasing said piston into said first position;

and

means for moving said piston into said second position in response tofluid flowing through said valve.

7. The transmission of claim 6 wherein said control valves additionallycomprise a spring for biasing said piston into said first position, saidpiston having a face opposed to said spring bias which communicates withsaid inlet for gradually moving said piston to said second position.

8. The transmission of claim 7 wherein said second face communicateswith said inlet by means of a restricted fluid passageway.

9. The transmission of claim 8 wherein the outlet from said firsthousing is connected in series with the outlet of said second housing.

1. A hydrostatic transmission with controlled acceleration comprising: apump for supplying pressurized fluid; a motor in fluid communicationwith said pump; a by-pass in fluid communication with said pump fordiverting a portion of the fluid from said pump away from said motor,said motor and said by-pass connected in parallel to said pump; andcontrol means in said by-pass for controlling the flow of fluid throughsaid by-pass, said means being normally open and operable to graduallyclose said by-pass and restrict fluid flow therethrough for graduallyincreasing the flow of fluid to said motor, said control meanscomprising: a housing having an inlet and an outlet connected in seriesin said by-pass, said housing having a first bore adjacent said inletand a larger bore adjacent said outlet, said first and larger boresbeing concentric and axially adjacent; a differential area piston havingfirst and second opposed faces of smaller and larger areas respectivelyslidably disposed within said bores, said piston biased by a spring andfluid pressure acting on said first face to a first position whereat thepiston allows fluid to flow from said inlet to said outlet, said pistonbiased by fluid pressure acting on said second face to graduallyovercome the bias of said spring and fluid pressure acting on the firstface to move to a second position whereat said inlet is blocked fromsaid outlet, said piston comprising axially adjacent first and largerexterior diameter sections slidably and sealingly engaged in said firstand larger bores respectively, said first section carrying said firstface and said larger section carrying said second face, said pistonhaving an axial bore communicating with said inlet and a radial borecommunicating said axial bore with the exterior surface of said firstsection, said radial bore communicating with said outlet in said firstposition and sealed by said first bore in said second position.
 2. Thetransmission of claim 1 wherein said piston additionally comprises arestricted fluid passageway communicating said axial bore with saidsecond face.
 3. The transmission of claim 1 wherein said pistoncomprises a larger exterior diameter section sealingly and slidablydisposed in said larger bore and an axially adjacent tapered section ofdecreasing cross-sectional diameter towards said inlet, said largerdiameter section carrying said second face and said tapered sectioncarrying said first face, said piston moving toward said inlet whenmoving from said first to said second position to form said variablyrestricted fluid flow orifice between the outer surface of said taperedsection and the interior of said first bore.
 4. The transmission ofclaim 3 wherein said piston additionally comprises a restricted fluidpassageway communicating said inlet and said second face.
 5. Ahydrostatic transmission having controlled acceleration comprising: areversible pump, a reversible motor, first and second fluid conduitsconnecting said pump to said motor; a first and second one-way by-passconnected in parallel around said motor, said first by-pass operable toby-pass fluid around the motor from said first to said second conduitwhen said first conduit is at a higher pressure than said secondconduit, said second by-pass operable to by-pass fluid around the motorfrom said second to said first conduit when said second conduit is at ahigher pressure than said first conduit, and a first and secondacceleration control valve for controlling the flow of fluid throughsaid first and second by-pass respectively, said control valvesconnected in series in said by-passes and being normally open andoperable to gradually close as fluid flows therethrough.
 6. Thetransmission of claim 5 wherein said control valves comprise: a hollowhousing having an inlet and an outlet, connected in series in saidby-passes, said housing having an axially adjacent smaller interiordiameter bore adjacent said inlet and a larger interior diameter boreadjacent said outlet; and a piston slidably disposed within said housingfor controlling the flow of fluid between said bores by providing avariably restricted fluid flow orifice therebetween, said piston in afirst position providing maximum fluid flow through said orifice and ina second position blocking said orifice; means for biasing said pistoninto said first position; and means for moving said piston into saidsecond position in response to fluid flowing through said valve.
 7. Thetransmission of claim 6 wherein said control valves additionallycomprise a spring for biasing said piston into said first position, saidpiston having a face opposed to said spring bias which communicates withsaid inlet for gradually moving said piston to said second position. 8.The transmission of claim 7 wherein said second face communicates withsaid inlet by means of a restricted fluid passageway.
 9. Thetransmission of claim 8 wherein the outlet from said first housing isconnected in series with the outlet of said second housing.